Re: Sourmash and yeast strains

I was reading up on this again and it appears many artisan distillers 1800's) added both backset and then actual fermentation lees to the the next mash, both to save the amount of fresh yeast needed for the next ferment and to improve flavor. You get lactic acid development which (as in some brewing) increases the complexity of the final spirit whether aged or white. One source said using only backset for the next mash was half of the original sourmashing process, i.e., that continued use of lees resulted in the best taste.

Reading all these old techniques, there is no surprise really that modern bourbon seems in general lighter and thinner than it was even in the 1970's.

Re: Sourmash and yeast strains

Originally Posted by tmckenzie

one major function you get from using backset is it is a yeast nutrient. Makes the yeast have something besides sugar to eat. If you do not use this, you have got to add nutrients to the mash. Which most micros do along with adding acid. There is no live yeast in it. dry yeast will work good, we however just installed a yeast tank last week and will be growing yeast from now on.

So the yeast eat other yeast? Does this happen when they're stressed, as well?

Re: Sourmash and yeast strains

the yeast sells will attch themselves to dead yeast cells, and the cells have burst due to heat. Releasing all of the nutrients they consumed during fermentation. Winemakers will use yeastex, which is dead yeast cells if yeast get stressed. You know they are stressed if they start producing sulfur. Which you can smell.

Re: Sourmash and yeast strains

Originally Posted by tmckenzie

the yeast sells will attch themselves to dead yeast cells, and the cells have burst due to heat. Releasing all of the nutrients they consumed during fermentation. Winemakers will use yeastex, which is dead yeast cells if yeast get stressed. You know they are stressed if they start producing sulfur. Which you can smell.

Sorry to keep this going, but I have read the hypothesis that the butterscotch flavor common to dusties came from stressed yeast. Do you have experience with that sort of flavor profile?

Re: Sourmash and yeast strains

Sorry to keep this going, but I have read the hypothesis that the butterscotch flavor common to dusties came from stressed yeast. Do you have experience with that sort of flavor profile?

You can get diacetyl (buttery aroma and flavor) as a by-product from yeast during fermentation under certain conditions - that is probably where it comes from. It is noticeable even at very low concentrations, and distillation would likely further concentrate any that was there.

Re: Sourmash and yeast strains

You can get butterscotch aromas much more so from small barrels too. Or at least we do. We don't sour mash, but we are playing around with doing some sour mash in the future.
I know some large distilleries that use a sweet mash to start after a shut down and then go back to the sour mash once the have stillage. Some also add some heads into the fermenter. Yeast seem to like low levels of ethanol.

Re: Sourmash and yeast strains

Sorry to keep this going, but I have read the hypothesis that the butterscotch flavor common to dusties came from stressed yeast. Do you have experience with that sort of flavor profile?

It would certainly make sense that some older production methods could lead to more diacetyl in the finished whiskey. The stressing that you refer to in some yeast strains doesn't lead to the yeast's production of diacetyl; rather, stressed yeast can lose its ability to reduce diacetyl and 2,3 Pentandion (same flavor) that is produced during fermentation. Since diacetyl is reduced at roughly the same rate as other maturation compounds in beer, diacetyl reduction is measured (sometimes by simply tasting the beer) by brewers to gauge the total maturation of aging beer.

The bulk of diacetyl is formed during primary fermentation.... in other words, just after the yeast is added to the mash and is in the first throes of fermentation. Once this diacetyl has been formed and is in the mash, the very same yeast cells begin to reduce this diacetyl by converting it to butanediol. Butanediol is flavorless.

A few things affect this reduction process (I won't bore you by listing them all). You need healthy happy yeast (this is where your stress question comes in), high temperatures (there in spades in a distiller's fermentation), and a low pH.

What can happen is that the yeast for various reasons (poor yeast management, mutations, underpitching, etc.) loses its ability to reduce the sometimes massive amounts of diacetyl that the primary fermentation generates. Combine this with very, very tight shortened fermentation times (counted by distillers in hours rather than days) that don't allow the yeast enough time to reduce the diacetyl.... and boom, there's your diacetyl in your finished whiskey.

Nowadays, big distilleries by and large use dry yeast, which almost eliminates errors in yeast management protocols that distillers of the past faced because the dry yeast has the same fermentation performance every time. Mutation and a reduction in the ability to reduce diacetyl is pretty much impossible with dry yeast.

As a side note, I'm sure you've heard of krauesening in German brewing production. Krauesening is a method of adding fresh yeast cells and wort to beer that's already almost completely fermented (kraeusen is added at about 10% of the volume of the beer that's being krauesened). What this does is add active yeast cells to rather cold beer in a cold fermenter. These healthy active yeast cells mop up the last bits of diacetyl that were not reduced because traditional lager fermentations are so cold that diacetyl reduction is rarely complete if you just add yeast at the start and that's it.

Another way you can get elevated VDK's (diacetyl & 2,3 Pentandion) is from bacterial infection, but that's a whole 'nother story, and I would find it unlikely to be the cause of butterscotchy whiskey.

The final way is simply because of yeast strain selection. Some strains famously produce a mess of it.... a couple of British Ale strains are notorious for it.